Limiting ring current in short circuits between adjacent partial windings by increasing leakage impedance

ABSTRACT

The invention relates to a method for regulating the electrical voltage in electrical supply networks and/or consumer units and a device for carrying out said method. A regulating transformer ( 3 ) is inserted between a network node ( 1 ) in the supply network and/or consumer unit and at least one end user ( 2 ). The regulating transformer ( 3 ) comprises a high leakage impedance, which limits the ring current to the order of magnitude of the nominal current, in the case of a short-circuit between adjacent tappings ( 5 ) of the partial windings ( 4 ). The regulating transformer further comprises a transfer switch ( 7 ), to switch the partial windings ( 4 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Stage of InternationalApplication No. PCT/AT00/00284 filed Oct. 31, 2000 and claims priorityunder 35 U.S.C. §119 of Austrian Patent Application No. A 1838/99 filedNov. 2, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for regulating the electrical voltagein electrical supply networks and/or consumer units and a device forcarrying out said method.

2. Discussion of Background Information

It is generally known to carry out voltage regulation only in thecentral network nodes of high or medium voltage networks. Furthertransformation to low-voltage level normally cannot be regulated underload. This network structure is oriented towards the central powersupply and has the disadvantage that voltage fluctuations caused by achange in node cannot be adjusted for between the network node and theend consumer. Thus, the exploitable transfer capacity of the networkcomponents downstream from the network nodes is limited by the drop involtage rather than by thermal strength.

Regulating transformers are provided for voltage regulation of thenetworks in the central network nodes. Regulating transformers are usedfor incremental voltage regulation in electrical networks by changingthe transformer ratio. For this purpose, regulating transformers arefitted with regulating windings with tappings, which can be switchedunder load. During the switching processes, the load current must not beinterrupted and the winding step between the relevant tappings must notbe shorted. The second requirement results from the fact that duringeach switching process between two neighbouring tappings they arenecessarily briefly connected to each other due to the firstrequirement, so that there is a ring current equivalent to thetransformer short-circuit current between the switch and the relevantwinding, the action of which the transformer is unable to withstand,especially during periodical operation. This transformer short-circuitcurrent is relatively high, since the internal resistance of thetransformer is normally small. Furthermore, the incremental switches ofthe transformers would have to be coordinated with the periodicalswitching of these high short-circuit currents.

For the above reasons, the switching process in the incremental switchof the transformer does not happen directly but rather in multiplestages, whereby transition impedances are briefly switched into thecircuits of the tappings during the switching process, limiting the ringcurrent. In Europe, ohmic transition impedances are common, and inAmerica inductive transition impedances are common. For multi-phaseswitching, a number of switching principles are applied that are namedafter the vector diagrams of the switching processes. For example wespeak of symmetrical or asymmetrical flag

SUMMARY OF THE INVENTION

The disadvantage of the measures used so far to limit the ring currentis that they result in complex transition principles and require complexdesigns of the regulating transformers.

The aim of this invention is therefore to create a method of the typementioned above that on the one hand avoids the above disadvantages andon the other hand allows or guarantees a better and more efficient useof the existing networks through a new field of voltage regulationapplication that is closer to the consumer.

The problem is solved by this invention.

The method in accordance with the invention is characterised by the factthat a regulating transformer with a transfer switch that switches thepartial windings of the regulating transformer is inserted between anetwork node of the supply network and/or the consumer unit and at leastone end consumer, whereby the regulating transformer has a high leakageimpedance that limits the ring current to the order of magnitude of thenominal current in the case of a short circuit between adjacenttappings.

With this invention it is for the first time possible to carry outvoltage regulation in networks or consumer units in proximity to theconsumer and on the basis of regulating transformers that have anincreased impedance of the regulating windings, so that a simplifiedstep switch without transition impedances can be used.

With the liberalisation and decentralisation of electric power supplyand due to the higher bi-directional work-load of the networks, thevoltage differences between heavy-duty consumption, low duty andpossibly the power supply will become greater on the consumer side. Tomaintain the voltage there should therefore be voltage regulation at thelevel of the low voltage or possibly at the level of the medium voltageas an economic solution.

It is a further aim of the invention to provide a device for carryingout this method, which has a simple and robust structure and which canbe manufactured economically.

According to a special feature of the invention, the device for carryingout the method is characterised by the fact that the regulatingtransformer is designed as a longitudinal regulator with a differentialcapacity that is proportional to the voltage difference that is to beregulated. In accordance with the invention, longitudinal regulators forvoltage maintenance are therefore provided in the network spurs, whichdo without the known and currently common transition impedances of thestep switch and thus the resistance contacts. This is primarily possiblebecause the voltage regulation is carried out at low-duty networkpoints. Even an increased impedance of such a longitudinal regulatorwill only have a marginal effect on the total internal resistance of thenetwork.

The need for transition impedances results from the fact that forreasons of voltage maintenance the internal network resistance andshort-circuit impedance of regulating transformers is much lower thanthe load impedance, so that the short-circuit currents are significantlyhigher than the operating currents.

If the short-circuit impedance of the regulator winding is increased,e.g. by widening the leakage gap, so that the ring circuit in the caseof a short circuit between adjacent tappings is of the order ofmagnitude of the nominal current, the additional transition impedancesare not required and the step switch is simplified into a normaltransfer switch.

The regulating winding can be designed both as a concentric winding andas a flat coil winding with the relevant tappings. This principle can beapplied both to full transformers with regulating winding and toone-coil transformers for longitudinal regulation. The regulatingwinding can be connected to the secondary winding or primary windingboth via one end of the winding and via a tapping.

Since the device is suitable for the voltage regulation of networkspurs, its capacity based on the transitional capacity lies within arange of a some 10 kVA to some 10 MVA.

In a further embodiment of the invention, the transfer switch is a loadswitch without resistance contact and with only main contacts. Asalready shown above, such a load transfer switch offers an economicalsolution.

In a further embodiment of the invention, the transfer switch is a loadselector without resistance contacts. This embodiment of the transferswitch also has an extremely simple structure and can be producedeconomically.

In further embodiments of the invention, the transfer switch can also bedesigned on the basis of a multi-phase camshaft controller or a chain ofrelays or contactors or a chain of electronic switches, in particularsemiconductor switches. These embodiments of the transfer switch alsohave a simple structure and are extremely reliable in robust operations.

The present invention is directed to a method to regulate electricvoltage in at least one of electric supply networks and consumer unitswith a regulating transformer located between a network node of the atleast one of the electric supply networks and the consumer units and atleast one end consumer, in which the regulating transformer hasswitchable partial windings. The process includes switching the partialwindings of the regulating transformer with a transfer switch. In thismanner, in an event of a short circuit between adjacent tappings of thepartial windings, the regulating transformer has a high leakageimpedance that limits ring current to an order of magnitude of a nominalcurrent.

The present invention is directed to an apparatus arranged to perform athe above-noted method.

According to the invention, the transfer switch can include a loadswitch without resistance contacts. Further, the load switch may includeonly main contacts.

In accordance with an other feature of the invention, the transferswitch may include a load selector, and the load selector can bearranged without resistance contacts.

Further, according to features present invention, the transfer switchmay include a multi-phase camshaft controller.

According to still another feature of the instant invention, thetransfer switch can include a chain of one of relays and contactors.

In accordance with yet another feature of the invention, the transferswitch may include a chain of electronic switches. The chain ofelectronic switches may include semiconductor switches.

The present invention is directed to an apparatus to regulate electricvoltage in at least one of electric supply networks and consumer unitsthat includes a regulating transformer, positioned between a networknode of the at least one of the electric supply networks and theconsumer units and at least one end consumer, that includes a pluralityof switchable partial windings, and a transfer switch arranged toselectively contact tappings of the switchable partial windings. Theregulating transformer includes a leakage gap such that, in the event ofa short circuit between adjacent tappings of the switchable partialwindings, the regulating transformer has a high leakage impedance thatlimits ring current to an order of magnitude of a nominal current.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail on the basis of the embodimentillustrated in the figure. The figures show:

FIG. 1 a basic sketch of the arrangement of a one-coil transformer

FIG. 2 a basic sketch of the arrangement of a full transformer

FIG. 3 a transfer switch based on contactors, and

FIG. 4 a transfer switch based on semiconductors.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

By way of introduction, it is noted that in the described embodiment thesame parts and the same states are allocated the same reference numbersand the same component names, whereby the disclosures containedthroughout the description can be applied by analogy to the same partsand the same states with the same reference numbers or same componentnames. Moreover, individual features from the embodiment illustrated canrepresent independent solutions according to the invention inthemselves.

FIG. 1 shows a device for regulating the electric voltage between onenetwork node 1—represented by the arrow—and one end consumer 2—alsorepresented by an arrow—whereby a regulating transformer 3 in the formof a one-coil transformer is provided for regulating the voltage. Thisone-coil transformer has a regulating winding with partial windings 4.The regulating winding is connected to the primary winding 6 of theone-coil transformer via a tapping 5, for example via a middle tapping.This allows both an increase and a decrease in voltage on the consumerside. The tappings 5 of the regulating winding are optionally connectedwith the output to the end consumer 2 via a transfer switch 7. Thetransfer switch 7 is controlled either via the control unit 8 withoutregulation or via a voltage controller 10 with regulation. Thetransitions are made in steps by closing a break adjacent to a closedbreak and then opening the original break. This allows the voltage onthe consumer side to be increased or decreased. In addition, anintegrated overvoltage protection 11 can be provided on the side of theend consumer 2.

To increase the short-circuit impedance of the regulating winding, theregulating transformer 3 in the embodiment as a one-coil transformer hasa widened leakage gap 9. Through this increase in leakage impedance, thering current is limited to the order of magnitude of the nominal currentin the case of a short circuit.

In FIG. 2 the device for regulating the electric voltage is againarranged between a network node 1 and an end consumer 2, whereby aregulating transformer 3 in the embodiment of a full transformer isprovided for regulation. Thereby, the connection between the regulatingwinding and the partial windings 4 is provided via one end of thesecondary winding of the regulating transformer 3. A transfer switch 7with control unit 8 is again provided at the partial windings 4. Toincrease the leakage impedance, the regulating transformer 3 again has awidened leakage gap 9. The leakage impedance of the secondary winding 14is not increased.

The transfer switch 7 is designed as a multi-phase camshaft controllerand corresponds with the tappings 5 of the partial windings 4.

As in the embodiment shown in FIG. 1, the regulating transformer 3 isdesigned as a longitudinal regulator and has a differential capacitythat is proportional to the voltage difference that is to be regulated.

In accordance with FIG. 3, the partial windings 4 with their tappings 5are connected with a series of contactors, which carry out the voltageregulation in accordance with the transfer switch 7 in FIGS. 1 and 2.The individual contactors 12 or relays are controlled via control units8 that are connected to a voltage regulator.

In accordance with FIG. 4, the partial windings 4 with their tappings 5are connected with a series of electronic switches 13, in particularsemiconductor switches, which carry out the voltage regulation inaccordance with the transfer switch 7 in FIGS. 1 and 2. The individualsemiconductor switches are controlled via electronic units that areconnected with the voltage regulator.

For form's sake, it is noted that for a better understanding of theinvention the components are illustrated partly untrue to scale and/orare enlarged and/or made smaller.

Moreover, individual features of the embodiment illustrated in thefigures in combination with other individual features or alone canrepresent independent solutions according to the invention inthemselves. In particular, the individual embodiments illustrated in thefigures can represent independent solutions according to the invention.The relevant tasks and solutions according to the invention are shown inthe detailed descriptions of these figures.

What is claimed is:
 1. An apparatus for regulating electric voltage inat least one of electric supply networks and consumer units, theapparatus comprising: a regulating transformer, conducting a nominalcurrent and positioned between a network node of the at least one of theelectric supply networks and the consumer units and at least one endconsumer, comprising a regulating winding with a plurality of switchablepartial windings; a transfer switch arranged to selectively contacttappings of said switchable partial windings, said regulatingtransformer comprising a leakage gap such that, in the event of a shortcircuit between adjacent tappings of said switchable partial windings,said regulating winding has a high leakage impedance that limits aresultant ring current to an order of magnitude of the nominal current.2. The apparatus in accordance with claim 1, wherein said transferswitch comprises a load switch without resistance contacts.
 3. Theapparatus in accordance with claim 2, wherein said load switch includesonly main contacts.
 4. The apparatus in accordance with claim 1, whereinsaid transfer switch comprises a load selector.
 5. The apparatus inaccordance with claim 4, wherein said load selector is arranged withoutresistance contacts.
 6. The apparatus in accordance with claim 1,wherein said transfer switch comprises a multi-phase camshaftcontroller.
 7. The apparatus in accordance with claim 1, wherein saidtransfer switch comprises a chain of one of relays and contactors. 8.The apparatus in accordance with claim 1, wherein said transfer switchcomprises a chain of electronic switches.
 9. The apparatus in accordancewith claim 8, wherein the chain of electronic switches comprisessemiconductor switches.
 10. A method of regulating an electric voltagein at least one of electric supply networks and consumer units with aregulating transformer located between a network node of the at leastone of the electric supply networks and the consumer units and at leastone end consumer, in which the regulating transformer conducts a nominalcurrent and has a regulating winding with switchable partial windings,the method comprising: switching the partial windings of the regulatingtransformer with a transfer switch, whereby, in an event of a shortcircuit between adjacent tappings of the partial windings, theregulating winding has a high leakage impedance that limits a resultantring current to an order of magnitude of the nominal current.
 11. Anapparatus arranged to perform the method in accordance with claim 10.12. The apparatus in accordance with claim 11, wherein the transferswitch comprises a load selector.
 13. The apparatus in accordance withclaim 12, wherein the load selector is arranged without resistancecontacts.
 14. The apparatus in accordance with claim 11, wherein thetransfer switch comprises a multi-phase camshaft controller.
 15. Theapparatus in accordance with claim 11, wherein the transfer switchcomprises a chain of one of relays and contactors.
 16. The apparatus inaccordance with claim 11, wherein the transfer switch comprises a chainof electronic switches.
 17. The apparatus in accordance with claim 16,wherein the chain of electronic switches comprises semiconductorswitches.
 18. The apparatus in accordance with claim 11, wherein thetransfer switch comprises a load switch without resistance contacts. 19.The apparatus in accordance with claim 18, wherein the load switchincludes only main contacts.